Electronically controlled direct fuel injection devices are well known in the art. Such devices include electronically controlled fuel injectors, which may be hydraulically or mechanically actuated. During an injection event, an electronically controlled fuel injector injects fuel into a combustion chamber in response to an electronic fuel injection signal produced by a controller. This signal includes a waveform indicative of an injection rate. The fuel injection waveform is tailored based on engine operating conditions. Specifically, the fuel injection waveform is tailored to include multiple fuel injections (hereafter “shots”) during each injection event. This use of multiple shots during each injection event may enable compliance with exhaust emissions regulations. These regulations restrict, for example, the emission of hydrocarbons and carbon monoxide, the release of particulates, and the release of nitrogen oxides (NOx). Each shot has specific attributes such as, for example, a duration and an injection rate. Shots are grouped, ordered, and timed to form shot modes, which correspond to fuel injection waveforms. Based on an engine speed and a desired quantity of fuel supplied to the engine, a shot mode is selected for each injection event. At different engine operating conditions, different shot modes are selected to achieve desired engine performances while complying with emissions regulations.
During normal operation of the engine, the selected shot mode may change several times. Typically, shot modes differ slightly in both noise level and torque produced. In some instances, transitioning from one shot mode to another causes a noticeable “step-change” in either or both of these characteristics and/or other characteristics. This sudden change in characteristics is undesirable.
One way to minimize the sudden change in characteristics is described in U.S. Pat. No. 6,371,077 (the '077 patent) issued to McGee on Apr. 16, 2002. The '077 patent describes a method for controlling a fuel injection control system to transition from one waveform to another. The method includes setting single check fuel hysteresis values, loop fuel hysteresis values, and engine speed hysteresis values. A potential waveform is determined from a lookup table or map, and a single check fuel change, an engine speed change, and a loop fuel value change are determined by comparing current fuel and engine speed values with previous fuel and engine speed values. If both the single check fuel change and engine speed change are greater than the respective hysteresis values in a single check, the active waveform is changed to the potential waveform. Additionally or alternatively, if the loop fuel value change is greater than the loop fuel hysteresis values for a repeated number of comparisons, the active waveform is changed to the potential waveform.
Although the method of the '077 patent may provide for a smooth transitioning from use of one waveform type to another waveform type by preventing repeated transfer back and forth between the waveforms, the method of the '077 patent may do little to allow for continuous transitioning of a fuel injection system between two shot modes. Failing to continuously transition the fuel injection system between two shot modes may decrease an efficiency of a combustion engine. For example, the combustion engine may operate on average at a higher or lower speed and/or fuel consumption than is desired.
The disclosed method and system are directed to improving prior systems.